The use of tubeless tires is widespread in the car sector. This kind of tire requires that the wheel rims onto which the said tires are mounted have a perfect pneumatic seal, and therefore requires careful verification of the wheel rims to discover any possible faults in construction which could compromise the maintaining of the pressure in the tires themselves. In particular, wheel rims cast in light alloys (aluminium and/or magnesium alloys) are subject to microporosity or microfissure.
Various systems are known for checking wheel rims. According to one known system the compactedness of the rim structure is tested by means of X rays; such a system is able to detect microfissures in the product, but is not able to verify whether such microfissures cause a defect in the seal.
A second known system comprise a sealing check by means of water, air or testing gas.
However, in such a system, checks are somewhat subjective. In addition, such a technique requires long checking times and therefore contributes to high production costs. U.S. Pat. No. 4,416,145 describes an apparatus and a method for detecting leakages in a container by applying gas under pressure to one of the container walls; the gas passes through any possible openings in the wall and causes bubbles in a high-surface tension liquid applied, causing the bubbles to burst, and makes ultrasounds; these are detected by an ultrasound transducer. Such patent, however, does not suggest using the present method for checking wheel rims and does not give any useful teaching concerning the present apparatus for checking wheel rims.